Temperature responsive apparatus



July 2, 1935. H MUELLER v 2 ,006,55

TEMPERATURE RESPONSIVE APPARATUS I Filed D60. 18, 1934 fivezzfort' A M s flilorneya Patented'July 2, 1935 TEMPERATURE nEsPoNsIvE Arrana'ms Hans Mueller, Brookline, Mass, assignor to Massachusetts Institute of Technology, Cam bridge, Mass., a corporation of Massachusetts Application December 18, 1934, Serial No. 758,147

Claims.

5 changes in temperature can be detected'and indicated at any desired point, either adjacent to or remote from the point where such changes occur, and which can also be employed, in a manner similar to a thermo-couple, to develop relatively high electric potentials as the-result of relatively small changes in temperature.

The invention is based on the discovery that if a crystal of Rochelle salt (which crystallizes in accordance with. the orthorhombic system) be includedin an electric circuit between two electrodes, with its c axis disposed. across the electrodes, 1. e., in the direction of the flow of current in the circuit, and thetemperature of the crystal changed, as by heating .or cooling, an electric potential is generated in the circuit. Experiments have shown that the potential developed varies as the square of the difference in temperature. The system is very responsive to even slight changes in temperature, a change of a very smallfraction (as small as one twentieth) of a degree centigrade resulting in a potential which can be detected by a suitable instrument, and a change of 5 'C.,.being sufflcient to cause a potential'which will produce a spark.

a The accompanying drawing is a diagrammatic view of a simple .iorm of apparatus in which the invention may be embodied and by which it may be practiced, although it will be understood that this is merely illustrative, and that the invention, as defined by the claims hereunto appended, maybe otherwise embodied and prac-' ticed without departure from its spirit and scope.

In the drawing, l0 denotes a crystal of Rochelle salt which may be either a complete crystal or a portion 0! such a crystal cut to a convenient size and shape. The crystal III is interposed bechange of temperature in the crystal ID will retween two electrodes II with its a axiscrossing said electrodes or dispwed transverse to their planes, as indicated. It is important that the contact between the crystal and the electrodes be as nearly perfectas possible, and to this end ing an electric circuit having included therein a.

the opposite faces of the crystal are preferably polished and'the electrodes made of tinfoil and.

cemented to said surface by athin coating of Canadian balsam. Graphite electrodes can he used if desired. The electrodes II are connected in an electric circuit l2 including an electrometer l3 or equivalent instrument capable of indieating and measuring electric potentials.

With the apparatus thus arranged, even slight suit in setting up in the circuit I! an electric potential which will be indicated by the instrument l3, the potential being substantially proportional to-the square of the change in temperature." The apparatus can therefore be used for many ofthe purposes of a thermocouple but is much simpler andmore responsive to slight changes in temperature than the ordinary thermocouple unless very elaborate and delicate appliances be employed in the latter. It can also be employed as .a thermometer to register changes of temperature in closed spaces or regions not conveniently accessible for direct observation, since the crystal with its electrodes can be positioned in such space or region and the instrument 13 located at some remote point where it can be conveniently read. It can further be used for many of the purposes of a photoelectric celi, since if a beam of radiant heat-l4,-

or a stream of heated air or other fluid, be projected from a suitable source l5 upon the crys--' tal to, any interruption or interception of said beam or stream will result in-a drop in the temperature of the crystal and a consequent change in the potential of the circuit which can be utilized in a variety of ways. These and many other uses and advantages of the invention will, how-- ever, be obvious without further discussion in detail.

I claim: a f

1. An apparatus for generating an electric potential in an electric circuit which comprises, a circuit, a crystal of Rochelle salt electrically connected therein and adapted to be subjected to changes in temperature.

2. A temperature measuring device comprising an electric circuit having included therein a pair of electrodes and an interposed crystal of.

crystal of Rochelle salt having opposite polished surfaces andftinfoil electrodes cemented to said surfaces, and -means for' indicating changes of potential in said circuit;

' 5 An apparatus for detecting changes in temperature which comprisesya circuit, a crystal of Rochelle salt electrically connected therein and adapted to be subjected to thechangesin temperature to be detected and means for indicating'chang'es of potential in' said circuit.

of potential in said 

